Variable voltage/variable frequency inverters have been put to practical use and followed by the development of the application areas for various kinds of power converters. For example, a three-phase voltage inverter or the like is used as a drive circuit in a motor driving device or the like. The three-phase voltage inverter includes a three-phase bridge circuit or the like with a semiconductor power-switching device such as a thyristor, a transistor, an IGBT, or a MOSFET. In this circuit, a switching element for each phase can be realized by directly connecting its positive and negative terminals to positive and negative terminals of a direct current (DC) voltage supply, respectively. In recent years, because of increasing efficiency of the device, an improvement in such a standard circuit has been facilitated to make the device more efficient.
Under the conventional technology, for example, there is proposed “a power converter including: a pair of main circuit switching elements that is to connected in series with a DC voltage source to supply power to a load; reverse current diodes connected reversely in parallel with the respective main circuit switching elements; and a reverse voltage application circuit that applies reverse voltage smaller than the DC voltage source to the respective reverse current diodes when each of these diodes is blocked” (see, for example, Patent Document 1).